Pneumatic tire

ABSTRACT

By forming a ground contact edge side of lug grooves such that the groove depth becomes shallower in groove depth from the tire equatorial plane side toward the ground contact edge, and by setting an average angle of inclination formed between a tread face and a groove bottom to be not more than 5°, water expulsion is performed smoothly in the vicinity of the ground contact edge while securing the rigidity of land portions in the vicinity of the ground contact edge. This enables a high degree of both wet performance and dry performance to be achieved.

TECHNICAL FIELD

The present invention relates to a pneumatic tire.

BACKGROUND ART

Conventional pneumatic tires are known in which lug grooves are formedin a tread in order to obtain water expelling performance (see, forexample, 1: Japanese National-Phase Publication No. 2008-308013).

SUMMARY OF INVENTION Technical Problem

Hitherto, pneumatic tires have demanded a high degree of both wetperformance, achieved through the water expelling performance ofgrooves, and dry performance, achieved through block rigidity.

There is a need for a groove depth of lug grooves to be deep in order toimprove the water expelling performance of the lug grooves, and a needfor a groove depth of lug grooves to be shallow in order to raise blockrigidity.

However, although simply setting lug grooves with a shallow groove depthin the vicinity of ground contact edges of a tread in order to securethe rigidity of shoulder-side land portions does raise the rigidity ofthe shoulder-side land portions, this is detrimental to water expellingperformance.

Moreover, if projections are provided at groove bottoms of the luggrooves as in the cited Patent Document, resistance arises when waterflows through, which could result in turbulent flow within the grooves,such that water does not flow smoothly.

In consideration of the above circumstances, an object of an embodimentof the present invention is to provide a pneumatic tire capable ofachieving a high degree of both wet performance and dry performance.

Solution to Problem

A pneumatic tire according to a first aspect includes a tread thatcontacts a road surface and plural lug grooves that are provided at thetread, that extend from a tire width direction center side of the treadtoward a ground contact edge of the tread, and that partition a landportion. When viewing a cross-section of each of the lug grooves along agroove length direction, in a state in which the tire is mounted to anapplicable rim and inflated to a maximum air pressure corresponding to atire standard maximum load capacity while applied with a load of 100% ofthe maximum load capacity in a state in which a tire rotation axis is,with respect to a horizontal and flat road surface, parallel to the roadsurface, each of the lug grooves includes a groove bottom formed at anincline with respect to a tread face of the tread contacting the roadsurface such that a groove depth at a ground contact edge side of thelug grooves becomes shallower in depth on progression from a tireequatorial plane side toward the ground contact edge. Moreover, anaverage angle of inclination θ1 formed between the tread face and thegroove bottom of the lug grooves from an intersection point P1 to anintersection point P3 is set to be no more than 5°. Wherein: P1 is anintersection point between the groove bottom of the lug grooves and animaginary line passing through the ground contact edge and extending ina direction at a right angle to the tread face, P3 is an intersectionpoint between the groove bottom of the lug grooves and an imaginary linepassing through a ⅓ point P2 on the tread face and extending in adirection at a right angle to the tread face, and P2 is ⅓ of thedistance of a tread half-width from the ground contact edge toward thetire equatorial plane side.

In the pneumatic tire according to the first aspect, the tread isprovided with the lug grooves formed such that the groove depth at theground contact edge side becomes shallower in depth on progression fromthe tire equatorial plane side toward the ground contact edge. Due tothe average angle of inclination θ1 of the groove bottom at the groundcontact edge side of the lug groove being set to be no more than 5°,when traveling on a wet road surface, this enables water that is takeninto the lug groove and that flows from the tire width direction centerside toward the ground contact edge of the tread to flow smoothly in thevicinity of the ground contact edge, to be expelled toward the outsideof the ground contact plane while securing the rigidity of the landportion in the vicinity of the ground contact edge.

A pneumatic tire according to a second aspect includes a tread thatcontacts a road surface, and plural lug grooves. The lug grooves areprovided at the tread, extend from a tire width direction center side ofthe tread toward a ground contact edge of the tread, and partition aland portion. When viewing a cross-section of each of the lug groovestaken along a groove length direction, in a state in which the tire ismounted to an applicable rim and inflated to a maximum air pressurecorresponding to a tire standard maximum load capacity while in anon-loaded state, each of the lug grooves has a groove bottom formed atan incline with respect to a tread face of the tread, such that a groovedepth at a ground contact edge side of the lug grooves becomes shallowerin depth on progression from a tire equatorial plane side toward theground contact edge. Moreover, an average angle of inclination θ2 formedbetween the tread face between the ground contact edge and a ⅓ point P2,and the groove bottom between an intersection point P1 and anintersection point P3, is set to be no more than 5°. Wherein: P1 is anintersection point between the groove bottom of the lug grooves and animaginary line passing through the ground contact edge and extending ina direction at a right angle to the tread face, P3 is an intersectionpoint between the groove bottom of the lug grooves and an imaginary linepassing through the ⅓ point P2 on the tread face and extending in adirection at a right angle to the tread face, and P2 is ⅓ of thedistance of a tread half-width from the ground contact edge toward atire equatorial plane side.

In the pneumatic tire according to the second aspect, the tread isprovided with the lug grooves formed such that the groove depth at theground contact edge side of the lug groove becomes shallower in depth onprogression from the tire equatorial plane side toward the groundcontact edge. Due to the average angle of inclination θ2 of the groovebottom at the ground contact edge side of the lug groove being set to beno more than 5°, when traveling on a wet road surface, this enableswater that is taken into the lug groove and that flows from the tirewidth direction center side toward the ground contact edge of the treadto flow smoothly in the vicinity of the ground contact edge and to beexpelled toward the outside of the ground contact plane.

A pneumatic tire according to a third aspect is the pneumatic tireaccording to the first aspect or the second aspect, wherein a flatportion having a constant groove depth from the ground contact edgetoward a tire width direction inner side is provided at the groovebottoms.

In the pneumatic tire according to the third aspect, due to providingthe groove bottom of the lug groove with the flat portion having aconstant groove depth from the ground contact edge toward a tire widthdirection inner side, this enables water to flow smoothly in the flatportion.

A pneumatic tire according to a fourth aspect is the pneumatic tire ofany one of the first aspect to the third aspect, wherein plural sipesare formed in the land portion including the ground contact edge, theplural sipes being formed so as to extend from a tire width directioninner side end of the land portion toward a tire width direction outerside and to traverse the ground contact edge, and at least half of thesipes out of the plural sipes are provided with a first raised-bottomportion having a height of from 2 mm to 4 mm within a range from theground contact edge to 20 mm toward the tire width direction inner side.

According to the pneumatic tire according to the fourth aspect, theplural sipes are formed in the land portion that includes the groundcontact edge. Due to at least half of the sipes out of the plural sipesbeing provided with the first raised-bottom portion having a height offrom 2 mm to 4 mm within a range from the ground contact edge to 20 mmtoward the tire width direction inner side, this enables rigidity on theground contact edge side of the land portion to be secured.

In the pneumatic tire according to the fourth aspect, sipes that areprovided with the first raised-bottom portion and sipes that are notprovided with the first raised-bottom portion are disposed alternately,enabling a configuration such that the first raised-bottom portions arenot adjacent to each other in the tire circumferential direction formutually adjacent sipes. This enables the effect of improved rigidity ofthe land portions due to the first raised-bottom portions to bemoderated between mutually adjacent sipes compared to cases in which thefirst raised-bottom portions are adjacent to each other in the tirecircumferential direction.

Moreover, in the pneumatic tire according to the fourth aspect, in casesin which sipes provided with the first raised-bottom portions areadjacent to each other, sipes provided with first raised-bottom portionshaving relatively low heights and sipes provided with firstraised-bottom portions having relatively high heights are disposedalternately. This enables the first raised-bottom portions having lowheights and the first raised-bottom portions having high heights aredisposed alternately to be disposed alternately to each other along thetire circumferential direction. This enables the effect of improvedrigidity of the land portions due to the first raised-bottom portions tobe moderated between mutually adjacent sipes compared to cases in whichthe first raised-bottom portion having high heights are adjacent to eachother in the tire circumferential direction.

A pneumatic tire according to a fifth aspect is the pneumatic tire ofany one of the first aspect to the fourth aspect, wherein the landportion partitioned by the plural lug grooves is further partitionedinto plural blocks in a tire width direction by plural circumferentialdirection grooves extending in a direction intersecting the lug grooves.Plural sipes are formed at blocks among the plurality of blocks thatinclude the ground contact edge. At least half of the plurality of sipesare provided with a second raised-bottom portion having a height of from2 mm to 5 mm within a range spanning from a tire width direction innerside end of the blocks to a position 40% of the distance from the tirewidth direction inner side end toward the ground contact edge of theblock.

In the pneumatic tire according to the fifth aspect, the plural sipesare formed at the blocks that include the ground contact edge. Du to atleast half of the sipes out of the plural sipes being provided with asecond raised-bottom portion having a height of from 2 mm to 5 mm withina range spanning from a tire width direction inner side end of the blocktoward the ground contact edge side as far as a position 40% of thedistance from the tire width direction inner side end to the groundcontact edge, this enables rigidity on the tire width direction innerside of the blocks to be secured.

In the pneumatic tire according to the fifth aspect, sipes that areprovided with the second raised-bottom portion and sipes that are notprovided with the second raised-bottom portion are disposed alternately,enabling a configuration such that the second raised-bottom portions arenot adjacent each other in the tire circumferential direction formutually adjacent sipes. This enables the effect of improved rigidity ofthe land portions due to the second raised-bottom portions to bemoderated between adjacent sipes compared to cases in which the secondraised-bottom portion are configured adjacent to each other in the tirecircumferential direction.

Moreover, in the pneumatic tire according to the fifth aspect, in casesin which sipes provided with the second raised-bottom portions areadjacent to each other, sipes provided with second raised-bottomportions having relatively low heights and sipes provided with secondraised-bottom portions having relatively high heights are disposedalternately. This enables the second raised-bottom portions having highheights and the second raised-bottom portions having low heights to bedisposed alternately to each other along the tire circumferentialdirection. This enables the effect of improved rigidity of the landportions due to the second raised-bottom portions to be moderatedbetween adjacent sipes compared to cases in which the secondraised-bottom portions having high heights are adjacent to each other inthe tire circumferential direction.

An angle of inclination of the lug groove with respect to the tire widthdirection may be set so as to be smaller on the ground contact edge sideof the tread than on the tire width direction center side of the tread.

Configuring the angle of inclination of the lug groove with respect tothe tire width direction so as to be smaller on the ground contact edgeside of the tread than on the tire width direction center side enableswater expelling performance to be improved compared to cases in whichthe angle of inclination of the lug groove with respect to the tirewidth direction is constant.

A change in the angle of inclination of the lug groove with respect tothe tire width direction may be made larger on the ground contact edgeside of the tread than on the tire width direction center side of thetread.

Making the change in the angle of inclination of the lug groove withrespect to the tire width direction larger on the ground contact edgeside of the tread than on the tire width direction center side enableswater expelling performance to be further improved.

A center circumferential direction groove disposed on the tireequatorial plane and extending along the tire circumferential directionmay be provided at the tread, and the lug grooves may extend from thecenter circumferential direction groove to the ground contact edge ofthe tread.

Since the center circumferential direction groove extends along the tirecircumferential direction, water taken into the groove can flowefficiently in the tire circumferential direction and be efficientlyexpelled toward the tire outside. Moreover, the center circumferentialdirection groove disposed on the tire equatorial plane can efficientlyexpel water in the vicinity of the center in the ground contact plane.

Moreover, since the lug grooves extend from the center circumferentialdirection groove to the ground contact edge of the tread, some of thewater taken into the center circumferential direction groove can beexpelled toward the ground contact edge outside of the tread via the luggrooves. This enables water expelling efficiency to be raised.

Herein, the “ground contact edge” of the present invention refers to atire width direction outermost position of a portion of a tread facethat contacts the road surface (contact patch shape) when a pneumatictire is mounted to a standard rim, as defined in the JATMA YEAR BOOK(Japan Automobile Tire Manufacturers Association standards), inflated toan internal pressure of 100% the air pressure (maximum air pressure)corresponding to the maximum load capacity (load shown in bold in theinternal pressure-load capacity correspondence table) for the applicableJATMA YEAR BOOK size/ply rating, when the maximum load capacity isapplied thereto. Note that in cases in which TRA standards or ETRTOstandards apply in the location of use or manufacturing location, thenthe respective standards are adhered to.

Advantageous Effects of Invention

The pneumatic tire according to the first aspect is capable of achievinga high degree of both wet performance and dry performance.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view illustrating a tread of a pneumatic tire accordingto a first exemplary embodiment of the present invention.

FIG. 2 is a cross-section taken along a tire rotation axis andillustrating one side of a pneumatic tire mounted to a rim and incontact with a road surface.

FIG. 3 is a cross-section taken along a tire rotation axis andillustrating one side of a pneumatic tire mounted to a rim and in anon-loaded state.

FIG. 4 is a cross-section illustrating a lug groove, taken along adirection orthogonal to the length direction of the lug groove.

FIG. 5 is a cross-section illustrating a lug groove of a pneumatic tireaccording to a second exemplary embodiment.

FIG. 6 is a cross-section illustrating a lug groove of a pneumatic tireaccording to a third exemplary embodiment.

FIG. 7 is a cross-section illustrating a lug groove, taken along thelength direction of the lug groove.

FIG. 8 is a plan view illustrating a third block.

FIG. 9 is a plan view illustrating a third block.

FIG. 10 is a plan view illustrating a third block.

FIG. 11 is a cross-section illustrating a lug groove, taken along adirection orthogonal to the length direction of the lug groove in apneumatic tire employed in testing.

DESCRIPTION OF EMBODIMENTS First Exemplary Embodiment

Explanation follows regarding a pneumatic tire 10 according to a firstexemplary embodiment of the present invention, with reference to thedrawings. Note that the pneumatic tire 10 of the present exemplaryembodiment is that of a passenger vehicle. The internal structure of thepneumatic tire 10 is similar to that of a conventional pneumatic tire,and so explanation thereof is omitted. In the drawings hereafter, thearrow A direction, the arrow B direction, and the arrow W directionrespectively indicate the tire rotation direction (tread-in side), theopposite direction to the tire rotation direction (kick-off side), andthe tire width direction.

As illustrated in FIG. 1, a tread 12 of the pneumatic tire 10 is formedwith a center circumferential direction groove 14 extending around thetire circumferential direction on a tire equatorial plane CL, and plurallug grooves 16 extending from the center circumferential directiongroove 14 toward ground contact edges 12E. Moreover, on the tread 12,shoulder-side circumferential direction grooves 20 are formed on bothtire width direction sides of the center circumferential directiongroove 14 so as to couple together one lug groove 16 and another luggroove 16 that are adjacent to each other in the tire circumferentialdirection. The center circumferential direction groove 14, the luggrooves 16, and the shoulder-side circumferential direction grooves 20are main grooves of the tread 12.

Each shoulder-side circumferential direction groove 20 of the presentexemplary embodiment is inclined with respect to the tirecircumferential direction such that an end portion on the tire rotationdirection side (arrow A direction side) is positioned further toward thetire width direction inner side than an end portion on the oppositedirection side to the tire rotation direction side (arrow B directionside).

On the tread 12, center-side blocks 22 are partitioned by the centercircumferential direction groove 14, the lug grooves 16, and theshoulder-side circumferential direction grooves 20, and shoulder-sideblocks 26 are partitioned by the shoulder-side circumferential directiongrooves 20 and the lug grooves 16.

On each center-side block 22 and shoulder-side block 26, plural sipes 28are formed extending in zigzags from a tire width direction inner sideend portion toward the tire width direction outer side. The depth of thesipes 28 of the present exemplary embodiment is set to 50% or greater ofthe groove depth of the lug grooves 16 (however, their maximum depth isno greater than the groove depth of the lug grooves 16).

Details Regarding the Lug Grooves

Each lug groove 16 of the present exemplary embodiment extends inclinedfrom the center circumferential direction groove 14 toward the groundcontact edge 12E. An angle of inclination θ0 of the lug groove 16 withrespect to the tire width direction gradually decreases on progressiontoward the ground contact edge 12E, and a groove width of the lug groove16 gradually increases on progression toward the ground contact edge12E. Further, the degree of change of the angle of inclination θ0 of thelug groove 16 with respect to the tire width direction is greater on theground contact edge 12E side than on the tire width direction centerside. Note that as illustrated in FIG. 1, the angle of inclination θ0 ofthe lug groove 16 with respect to the tire width direction is an angleof inclination of a tangent to a groove width center line GCL of the luggroove 16 with respect to the tire width direction.

Note that the lug groove 16 may be formed parallel to the tire widthdirection, or may extend inclined at a constant angle with respect tothe tire width direction. Further, the groove width of the lug groove 16may be constant from the center circumferential direction groove 14 tothe ground contact edge 12E.

Cross-Section Profile of Lug Groove Along Length Direction

As illustrated in FIG. 2, when viewing the cross-section of the luggroove 16 taken along its groove length direction (groove width centerline GCL) in a state in which the pneumatic tire 10 of the presentexemplary embodiment is mounted to an applicable rim 30, and inflated tothe maximum air pressure corresponding to the tire standard (JATMA inthe present exemplary embodiment) maximum load (maximum load capacity)while applied with a load of 100% of the maximum load in a state inwhich and the tire rotation axis is, with respect to a horizontal andflat road surface 31, parallel to the road surface, a groove bottom 16Bis inclined with respect to a tread face 12A contacting the road surface31 such that the groove depth in the vicinity of the ground contact edge12E of the lug groove 16 becomes gradually shallower in groove depth onprogression from the tire equatorial plane CL side toward the groundcontact edge 12E. On the tire equatorial plane CL side, the groovebottom 16B is formed with a constant groove depth parallel with respectto the tread face 12A contacting the road surface 31. Note that in FIG.2, the center circumferential direction groove 14 and the shoulder-sidecircumferential direction grooves 20 are omitted from illustration.

With regard to the lug groove 16, the groove bottom 16B of the luggroove 16 from an intersection point P1 to an intersection point P3 isset such that an average angle of inclination θ1 with respect to thetread face 12A contacting the road surface 31 is no more than 5°,wherein P1 is an intersection point of an imaginary line FL1 passingthrough the ground contact edge 12E and extending in a direction at aright angle to the tread face 12A contacting the road surface 31 withthe groove bottom 16B (at a groove width center) of the lug groove 16,and P3 is an intersection point of an imaginary line FL2 passing througha ⅓ point P2 on the tread face 12A ⅓ of the distance of a treadhalf-width ½ TW from the ground contact edge 12E toward the tireequatorial plane CL side and extending in a direction at a right angleto the tread face 12A contacting the road surface 31 with the groovebottom 16B of the lug groove 16. Note that the lug groove 16 has aconstant groove depth from the ⅓ point P2 across to the tire equatorialplane CL end portion thereof.

Note that with regard to the groove depth of the lug groove 16, there isno increase in the groove depth of the lug groove 16 from theintersection point P3 to the intersection point P1, since this woulddecrease the rigidity in the vicinity of the ground contact edge 12E ofthe tread 12. Note that “rigidity” in the present exemplary embodimentrefers to compression rigidity.

Further, the groove depth of the lug groove 16 at the ground contactedge 12E is the same depth or shallower than at the end portion on thetire equatorial plane CL side. However, the groove depth at the groundcontact edge 12E is preferably within a range of 50% to 100% of themaximum groove depth on the tire equatorial plane CL side. When thegroove depth at the ground contact edge 12E is less than 50% of themaximum groove depth on the tire equatorial plane CL side, the groovedepth of the lug groove 16 is too shallow, and water expellingperformance decreases. On the other hand, when the groove depth at theground contact edge 12E is over 100%, the groove depth of the lug groove16 is too deep, and there is concern regarding block rigidity in thevicinity of the ground contact edge 12E decreasing.

Note that the cross-section profile of the lug groove 16 taken along itsgroove length direction is explained based on FIG. 2 for a state inwhich the pneumatic tire 10 is applied with a load and is contacting theroad surface; however, explanation follows regarding a case in which thepneumatic tire 10 is in a non-loaded state.

FIG. 3 illustrates a cross-section of the lug groove 16 taken along itsgroove length direction when the pneumatic tire 10 of the presentexemplary embodiment is mounted to the applicable rim 30, inflated tothe maximum air pressure corresponding to the maximum load (maximum loadcapacity) in the tire standard (JATMA in the present exemplaryembodiment) while not applied with a load. As illustrated in FIG. 3, inthe vicinity of the ground contact edge 12E, the groove depth of the luggroove 16 becomes gradually shallower in groove depth on progressionfrom the tire equatorial plane CL side toward the ground contact edge12E, and on the tire equatorial plane CL side, the groove depth isconstant. Note that in FIG. 3, the center circumferential directiongroove 14 and the shoulder-side circumferential direction grooves 20 areomitted from illustration.

With regard to the lug groove 16, an average angle of inclination θ2between the groove bottom 16B between an intersection point P1 and theintersection point P3, and the tread face 12A between the ground contactedge 12E and the ⅓ point P2, is set to no more than 5°, wherein theintersection point between the imaginary line FL1 passing through theground contact edge 12E and extending in a direction at a right angle tothe tread face 12A with the groove bottom 16B (at the groove widthcenter) of the lug groove 16 is P1, and the intersection point betweenthe imaginary line FL2 passing through the ⅓ point P2 on the tread face12A ⅓ of the distance of the tread half-width ½ TW from the groundcontact edge 12E toward the tire equatorial plane CL side and extendingin a direction at a right angle to the tread face 12A with the groovebottom 16B of the lug groove 16 is P3.

As illustrated in FIG. 4, the lug groove 16 of the present exemplaryembodiment is formed with an asymmetrical profile on the tire rotationdirection side (arrow A direction side) and the opposite direction sideto the tire rotation direction side (arrow B direction side) of thegroove width (W0) center line GCL.

As illustrated in FIG. 4, in the lug groove 16, on either side of aposition P4 at a depth of ½ the groove depth D of the lug groove 16, agroove side-wall 16F on the tread-in side of each block is configured bya tread-in side first inclined portion 16Fa on the tread face 12A side,and a tread-in side second inclined portion 16Fb on the groove-bottomside. On the other hand, on the other side of the groove width centerline GCL, on either side of a position P5 at a depth of ½ the groovedepth D of the lug groove 16, a groove side-wall 16K on the kick-offside is configured by a kick-off side first inclined portion 16Ka on thetread face 12A side, and a kick-off side second inclined portion 16Kb onthe groove-bottom side.

In the lug groove 16, a width dimension of the tread-in side firstinclined portion 16Fa measured along the groove width direction is W1, awidth dimension of the tread-in side second inclined portion 16Fbmeasured along the groove width direction is W2, a width dimension ofthe kick-off side first inclined portion 16Ka measured along the groovewidth direction is W3, and a width dimension of the kick-off side secondinclined portion 16Kb measured along the groove width direction is W4.

Note that the width dimension W2 of the tread-in side second inclinedportion 16Fb and the width dimension W4 of the kick-off side secondinclined portion 16Kb are preferably set within a range of from 20% to50% of the groove width W0 of the lug groove 16.

Note that the groove bottom 16B refers to the deepest portion of the luggroove 16. When viewing a cross-section of the lug groove 16 takenorthogonal to the length direction of the lug groove 16, sometimes thegroove bottom 16B has a groove width direction dimension, as illustratedin the example of FIG. 4, and sometimes the groove bottom 16B does nothave a groove width direction dimension, as illustrated in the exampleof FIG. 6.

Let an imaginary line passing through an end portion on the tread face12A side of the tread-in side first inclined portion 16Fa andperpendicular to the tread face 12A be FL3. Let an imaginary linepassing through an end portion on the tread face 12A side of thetread-in side second inclined portion 16Fb (=the position P4 at a depthof ½ the groove depth D; an end portion on the groove-bottom side of thetread-in side first inclined portion 16Fa) and perpendicular to thetread face 12A be FL4. Let an imaginary line passing through an endportion on the tread face 12A side of the tread-in side second inclinedportion 16Fb (=the position P4 at a depth of ½ the groove depth D) andextending along the groove width direction be FL5. Let an imaginary linepassing through the deepest portion of the lug groove 16 (anintersection point P6 of the groove width center line GCL with thegroove bottom 16B) and extending along the groove width direction beFL6. Then A1 is set to be less than B1, where A1 is defined as the areaof a substantially triangular region (portion with a diagonal linetoward the upper right) enclosed by the imaginary line FL3, theimaginary line FL5, and the tread-in side first inclined portion 16Fa,and B1 is defined as the area of a substantially triangular region(portion with a diagonal line toward the upper left) enclosed by theimaginary line FL4, the imaginary line FL6, and the tread-in side secondinclined portion 16Fb. Note that the ratio B1/A1 between B1 and A1 ispreferably set to 120% or more, is more preferably set to 180% or moreto increase the block rigidity, and is even more preferably set to 270%or more. The practical upper limit of the ratio B1/A1 is 500%. However,the upper limit of the ratio B1/A1 may be unbounded (∞: when A1 is 0(for example, when the tread-in side first inclined portion 16Fa is at aright angle to the tread face 12A)).

Setting A1<B1 enables the block rigidity to be raised on thegroove-bottom side of the groove side-wall 16F on the tread-in side ofeach block while securing the groove volume of the lug grooves 16.Raising the block rigidity on the groove-bottom side of the grooveside-wall 16F on the tread-in side of each block enables the blockrigidity of the entire tread-in side of each block to be raised.

Note that the ratio B1/A1 between B1 and A1 is preferably set to 120% ormore to further increase the block rigidity, is more preferably set to180% or more to increase the block rigidity even further, and is evenmore preferably set to 270% or more. The practical upper limit of theratio B1/A1 is 500%. However, the upper limit of the ratio B1/A1 may beunbounded (∞: when A1 is 0 (for example, when the tread-in side firstinclined portion 16Fa is at a right angle to the tread face 12A)).

Further, let an imaginary line passing through an end portion on thetread face 12A side of the kick-off side first inclined portion 16Ka andperpendicular to the tread face 12A be FL7, and let an imaginary linepassing through an end portion on the tread face 12A side of thekick-off side second inclined portion 16Kb (=the position P5 at a depthof ½ the groove depth D; an end portion on the groove-bottom side of thekick-off side first inclined portion 16Ka) and perpendicular to thetread face 12A be FL8. Then A2 is set to be less than B2, where A2 isdefined as the area of a substantially triangular region (portion with adiagonal line toward the upper right) enclosed by the imaginary lineFL7, the imaginary line FL5, and the kick-off side first inclinedportion 16Ka, and B2 is defined as the area of a substantiallytriangular region (portion with a diagonal line toward the upper left)enclosed by the imaginary line FL8, the imaginary line FL6, and thekick-off side second inclined portion 16Kb. Note that the ratio B2/A2between B2 and A2 is preferably set to 120% or more, is more preferablyset to 180% or more to increase the block rigidity, and is even morepreferably set to 270% or more. The practical upper limit of the ratioB2/A2 is 500%. However, the upper limit of the ratio B2/A2 may beunbounded (∞: when A2 is 0 (for example, when the kick-off side firstinclined portion 16Ka is at a right angle to the tread face 12A)).

Setting A2<B2 enables the block rigidity to be raised on thegroove-bottom side of the groove side-wall 16K on the kick-off side ofthe center-side blocks 22 and the shoulder-side blocks 26 while securingthe groove volume of the lug grooves 16. Raising the block rigidity onthe groove-bottom side of the groove side-wall 16K on the kick-off sideof each block enables the block rigidity of the entire kick-off side ofeach block to be raised.

Further, in the present exemplary embodiment, when comparing the ratioB1/A1 to the ratio B2/A2, the ratio B1/A1 is set to be less than theratio B2/A2. The block rigidity on the kick-off side is thereby raisedto a greater extent than the block rigidity on the tread-in side of thecenter-side blocks 22 and the shoulder-side blocks 26.

Moreover, in the lug groove 16 of the present exemplary embodiment, aradius of curvature Ra of a circular arc shaped portion of the tread-inside second inclined portion 16Fb and a radius of curvature Rb of acircular arc shaped portion of the kick-off side second inclined portion16Kb increase on progression from the tire equatorial plane CL sidetoward the ground contact edge 12E. As a result, the width dimension W2of the tread-in side second inclined portion 16Fb and the widthdimension W4 of the kick-off side second inclined portion 16Kb increase,and the area B1 and the area B2 increase on progression from the tireequatorial plane CL side toward the ground contact edge 12E. The blockrigidity on the tread-in side and the block rigidity on the kick-offside of the center-side blocks 22 and the shoulder-side blocks 26thereby increase on progression from the tire equatorial plane CL sidetoward the ground contact edge 12E.

Operation and Advantageous Effects

In conventional pneumatic tires, groove side-walls of groovespartitioning blocks are inclined in their entirety to increase blockrigidity. However, this decreases the volume of the grooves anddecreases wet performance, such that it is difficult to achieve both ahigh degree of block rigidity and a high degree of wet performance. Incontrast, the pneumatic tire 10 of the present exemplary embodiment canachieve both a high degree of block rigidity and a high degree of wetperformance. Explanation follows regarding operation and advantageouseffects of the pneumatic tire 10 of the present exemplary embodimentwhen mounted to a vehicle.

When the pneumatic tire 10 is traveling on a wet road surface, water inthe plane of ground contact (water between the tread face 12A of thetread 12 and the road surface) is taken into the center circumferentialdirection groove 14, the lug grooves 16, and the shoulder-sidecircumferential direction grooves 20, and expelled to the tirecircumferential direction outside by the center circumferentialdirection groove 14 and the shoulder-side circumferential directiongrooves 20 and expelled to the tire width direction outer side by thelug grooves 16. Note that some of the water that has been taken in tothe center circumferential direction groove 14 and the shoulder-sidecircumferential direction grooves 20 is expelled to the tire widthdirection outer side by the lug grooves 16. The pneumatic tire 10 of thepresent exemplary embodiment obtains wet performance by expelling thewater in the plane of ground contact in this manner. Further, in thepneumatic tire 10 of the present exemplary embodiment, the centercircumferential direction groove 14 extending along the tirecircumferential direction is disposed on the tire equatorial plane CL,enabling water expelling performance to be raised at a tire centersection where contact pressure with the ground is high.

On the tread-in side of each block of the pneumatic tire 10 of thepresent exemplary embodiment, when comparing the area A1 of thesubstantially triangular region enclosed by the imaginary line FL3, theimaginary line FL5, and the tread-in side first inclined portion 16Faagainst the area B1 of the substantially triangular region enclosed bythe imaginary line FL4, the imaginary line FL6, and the tread-in sidesecond inclined portion 16Fb, A1 is set to be less than B1. This enablesrigidity to be raised on the groove-bottom side of the tread-in side ofeach block (namely, a base portion on the tread-in side of each block)of the center-side blocks 22 and the shoulder-side blocks 26, therebyenabling block rigidity to be raised on the tread-in side of each blockwhile securing the groove volume necessary for water expellingperformance of the lug grooves 16.

Moreover, on the kick-off side of each block of the pneumatic tire 10 ofthe present exemplary embodiment, when comparing the area A2 of thesubstantially triangular region enclosed by the imaginary line FL7, theimaginary line FL5, and the kick-off side first inclined portion 16Kaagainst the area B2 of the substantially triangular region enclosed bythe imaginary line FL8, the imaginary line FL6, and the kick-off sidesecond inclined portion 16Kb, A2 is set to be less than B2. This enablesrigidity to be raised on the groove-bottom side of the kick-off side ofeach block (namely, a base portion on the kick-off side of each block),thereby enabling block rigidity to be raised on the kick-off side ofeach block while securing the groove volume necessary for waterexpelling performance of the lug grooves 16.

As explained above, in the pneumatic tire 10 of the present exemplaryembodiment, the block rigidity on the tread-in side and the blockrigidity on the kick-off side of each block are raised, enabling theblock rigidity of the overall block necessary for steering stability ona dry road surface to be increased. Further, in the pneumatic tire 10 ofthe present exemplary embodiment, the groove side-walls are not inclinedin their entirety to raise block rigidity, which would increase theamount of rubber used in the tread 12. This thereby enables an increasein roll resistance to be suppressed.

In this manner, the pneumatic tire 10 of the present exemplaryembodiment can achieve a high degree of both wet performance and dryperformance by obtaining wet performance (hydroplaning performance inparticular) and dry performance (steering stability on a dry roadsurface in particular). Further, by suppressing deformation of eachblock of the center-side blocks 22 and the shoulder-side blocks 26, dragof the blocks against the road surface can be suppressed, enablinganti-wear characteristics of the blocks to be improved.

Moreover, in the pneumatic tire 10 of the present exemplary embodiment,the ratio B1/A1 is set to be less than the ratio B2/A2, and the blockrigidity on the kick-off side is raised to a greater extent than theblock rigidity on the tread-in side of each of the blocks configuringthe center-side blocks 22 and the shoulder-side blocks 26. Thus,compared to cases in which the block rigidity on the tread-in side israised to a greater extent than the block rigidity on the kick-off side,tire circumferential direction deformation can be effectively suppressedwhen the pneumatic tire 10 rotates in the arrow A direction (whendriving) and each block contacts the road surface.

Further, in the pneumatic tire 10 of the present exemplary embodiment,the radius of curvature Ra of the circular arc shaped portion of thetread-in side second inclined portion 16Fb and the radius of curvatureRb of the circular arc shaped portion of the kick-off side secondinclined portion 16Kb of the lug groove 16 increase on progression fromthe tire equatorial plane CL side toward the ground contact edge 12Esuch that area B1 and area B2 increase on progression from the tireequatorial plane CL side toward the ground contact edge 12E. Thisenables block rigidity on the tread-in side and the block rigidity onthe kick-off side of the center-side blocks 22 and the shoulder-sideblocks 26 to increase on progression from the tire equatorial plane CLside toward the ground contact edge 12E. Accordingly, when a large loadis borne on the shoulder side, namely the ground contact edge 12E side,of the tread during cornering, deformation of the shoulder-side blocks26 on the ground contact edge 12E side can be effectively suppressed,enabling cornering performance to be improved while securing groovevolume on the ground contact edge 12E side of the lug grooves 16.

The lug-groove bottom side of the tread-in side second inclined portion16Fb and the lug-groove bottom side of the kick-off side second inclinedportion 16Kb are formed in circular arc shapes. Thus, stress issuppressed from concentrating at the groove bottom 16B of the lug groove16, and cracks starting from the groove bottom 16B are suppressed fromoccurring. Moreover, water expelling performance is improved becausewater flow tends to be laminar flow rather than turbulent flow whenwater flows within the lug groove 16.

The width dimension W2 of the tread-in side second inclined portion 16Fband the width dimension W4 of the kick-off side second inclined portion16Kb are set within a range of from 20% to 50% of the groove width W0 ofthe lug groove 16, thereby enabling a high degree of both block rigidityand water expelling performance to be achieved. Note that when theproportion of the width dimension W2 and the proportion of the widthdimension W4 with respect to the groove width W0 of the lug groove 16 isless than 20%, it becomes difficult to sufficiently increase the blockrigidity. On the other hand, when the proportion of the width dimensionW2 and the proportion of the width dimension W4 with respect to thegroove width W0 of the lug groove 16 exceeds 50%, it becomes difficultto secure sufficient volume for the lug grooves 16. Further, makingeither one of the width dimension W2 or the width dimension W4 too largewould make it impossible to increase the size of the other.

Note that the angle of inclination θ0 of the lug groove 16 with respectto the tire width direction gradually decreases on progression towardthe ground contact edge 12E, and moreover, the change in the angle ofinclination θ0 of the lug groove 16 with respect to the tire widthdirection is larger at the ground contact edge 12E side than at the tirewidth direction center side. The direction in which the lug groove 16extends accordingly approaches the direction in which water between thetread 12 and the road surface readily flows toward the outside of theground contact plane. This enables water expelling performance to beimproved and wet performance to be improved.

The lug groove 16 causes water taken into the plane of ground contactwhen traveling on a wet road surface to flow from the tire equatorialplane CL side toward the ground contact edge 12E side, and expels thewater from the end portion on the ground contact edge 12E side to thetire outside. In the vicinity of the ground contact edge 12E, the groovebottom 16B is inclined such that the groove depth of the lug groove 16gradually becomes shallower on progression toward the ground contactedge 12E, and the angle of inclination θ1 of the groove bottom 16B isset to no more than 5°. Water that has been taken into the groove canthereby be made to flow smoothly toward the ground contact edge 12E andbe expelled in the vicinity of the ground contact edge 12E, therebyenabling wet performance to be improved. Further, the groove width ofthe lug groove 16 of the present exemplary embodiment widens onprogression from the tire equatorial plane CL side toward the groundcontact edge 12E side. This, too, enables water expelling performancefrom the tire equatorial plane CL side toward the ground contact edge12E side to be improved, thereby enabling wet performance to be furtherimproved.

Further, in the pneumatic tire 10 of the present exemplary embodiment,in the vicinity of the ground contact edge 12E, the groove bottom 16B isinclined such that the groove depth of the lug groove 16 graduallybecomes shallower on progression toward the ground contact edge 12E.There is accordingly no concern of block rigidity decreasing as therewould be in a case in which the groove bottom 16B is inclined such thatthe groove depth of the lug groove 16 gradually becomes deeper onprogression toward the ground contact edge 12E, and so block rigidity inthe vicinity of the ground contact edge 12E necessary for dryperformance is secured. A high degree of both wet performance and dryperformance can be achieved by setting the angle of inclination θ1 ofthe groove bottom 16B of the lug groove 16 to no more than 5° in thismanner.

Note that in the pneumatic tire 10 of the present exemplary embodiment,preferably a<c is satisfied, where a (mm²) is the cross-sectional areaat a connection portion of the lug groove 16 to the centercircumferential direction groove 14 and c (mm²) is a cross-sectionalarea of the lug groove 16 at the ground contact edge 12E. This isbecause setting a small cross-sectional area a on the entry side ofwater flowing into the lug groove 16 and setting a largercross-sectional area c on the exit side of water flowing in the luggroove 16 enables turbulent flow to be suppressed from occurring as aresult of an increase in the amount of water due to water from thecenter circumferential direction groove 14 converging with the luggroove 16, enabling water expelling performance in which the lug groove16 acts as one main water flow path to be improved, and thus enablingwater expelling performance of the pneumatic tire 10 to be improved.Specifically, the groove width of the lug groove 16 is preferably from 0mm to 2.0 mm at the tread width direction inner side end portion, and ispreferably from 9.0 mm to 12.0 mm at the ground contact edge 12E.

Preferably b<c is satisfied, where b (mm²) is the cross-sectional areaof a connecting portion between one tire circumferential direction sideend portion of the shoulder-side circumferential direction groove 20 andthe lug groove 16. This is because turbulent flow can be suppressed fromoccurring as a result of an increase in the amount of water due to waterfrom the shoulder-side circumferential direction groove 20 convergingwith the lug groove 16, thereby enabling water expelling performance inwhich the lug groove 16 acts as a main water flow path to be furtherimproved. For similar reasons, the ratio b/c is preferably 0.60 or less,and is even more preferably 0.42 or less. On the other hand, the ratiob/c is preferably 0.07 or more in order to secure the amount of waterexpelled from the shoulder-side circumferential direction grooves 20.

The cross-sectional area a is preferably from 0 mm² to 18 mm². This isbecause setting the cross-sectional area a to 0 mm² or greater enablestraction on snow to be improved, while setting the cross-sectional areaa to no more than 18 mm² suppresses turbulent flow from occurring asdescribed above, and enables water expelling performance in which thelug groove 16 acts as a main water flow path to be further improved.

Further, the cross-sectional area b is preferably from 8 mm² to 46 mm².This is because setting the cross-sectional area b to no less than 8 mm²enables snow clogging to be suppressed and the amount of water expelledfrom a circumferential direction groove 3 b to be secured, while settingthe cross-sectional area b to no more than 46 mm² suppresses turbulentflow from occurring as described above, and enables water expellingperformance in which the lug groove 16 acts as a main water flow path tobe further increased.

Moreover, the cross-sectional area c is preferably from 77 mm² to 110mm². This is because setting the cross-sectional area c to no less than77 mm² secures the amount of water flowing in the lug groove 16, thisbeing the main water flow path, thereby enabling water expellingperformance to be improved, while setting the cross-sectional area c tono more than 110 mm² secures ground contact surface area, thus enablingdry road surface travel performance and the like to be secured.

Note that in the pneumatic tire 10 of the present exemplary embodiment,the ratio B1/A1 is set to be less than the ratio B2/A2, such that theblock rigidity on the kick-off side is raised to a greater extent thanthe block rigidity of the tread-in side of each block configuring thecenter-side blocks 22 and the shoulder-side blocks 26. However, thepresent invention is not limited thereto. The ratio B1/A1 may be set tobe greater than the ratio B2/A2, such that the block rigidity on thetread-in side is raised to a greater extent than the block rigidity ofthe kick-off side of each block configuring the center-side blocks 22and the shoulder-side blocks 26.

Further, in the tread 12, in cases in which, for example, bothshoulder-side blocks 26 having a long circumferential directiondimension and shoulder-side blocks 26 having a short circumferentialdirection dimension are present, the shoulder-side blocks 26 having ashort circumferential direction dimension have less block rigidityrelative to the shoulder-side blocks 26 having a long circumferentialdirection dimension. In such cases, it is preferable that the rigidityof the groove side-walls on the side of the shoulder-side blocks 26having a short circumferential direction dimension be raised to agreater extent than the rigidity of the groove side-walls on the side ofthe shoulder-side blocks 26 having a long circumferential directiondimension by, for example, employing a method to make the radius ofcurvature Ra on the tread-in side and the radius of curvature Rb on thekick-off side of the lug grooves 16 partitioning the shoulder-sideblocks 26 having a short circumferential direction dimension larger thanthe radius of curvature Ra on the tread-in side and the radius ofcurvature Rb on the kick-off side of the lug grooves 16 partitioning theshoulder-side blocks 26 having a long circumferential directiondimension. Thus, while still securing the groove volume of the luggrooves 16, the advantageous effect of increasing the block rigidity ofthe shoulder-side blocks 26 having a short circumferential directiondimension is greater than the advantageous effect of increasing theblock rigidity of the shoulder-side blocks 26 having a longcircumferential direction dimension. This thereby enables the differencein block rigidity to be reduced between the shoulder-side blocks 26having a short circumferential direction dimension and the shoulder-sideblocks 26 having a long circumferential direction dimension.

It is sufficient that the lug grooves 16 extend in the tire widthdirection or extend inclined at an angle of no more than 45° withrespect to the tire width direction. Water expelling performance can beincreased by extending the lug grooves 16 along the direction in whichwater flows during tire rotation. The groove depth (maximum depth) ofthe lug groove 16 is preferably from 1.0 mm to 9.2 mm in order to securethe groove volume to expel water. The lug grooves 16 are preferablydisposed at a pitch interval of from 16 mm to 20 mm in the tirecircumferential direction in order to achieve a high degree of bothwater expelling performance, and braking performance and steeringstability on dry road surfaces and icy/snowy road surfaces. Asillustrated in FIG. 1, the lug grooves 16 are preferably disposed with aphase difference around the tread circumferential direction impartedbetween one tire width direction side and the other tire width directionside of the tire equatorial plane CL, in order to decrease patternnoise.

The shoulder-side circumferential direction groove 20 preferably extendsin the tire circumferential direction or extends inclined at an angle of0° or greater, but less than 45°, with respect to the tirecircumferential direction in order to achieve a high degree of bothwater expelling performance, and steering stability on icy/snowy roadsurfaces. The groove width of the shoulder-side circumferentialdirection groove 20 is preferably from 2.0 mm to 10.0 mm in order toachieve a high degree of both water expelling performance, and brakingperformance and steering stability on dry road surfaces and icy/snowyroad surfaces. The groove depth (maximum depth) of the shoulder-sidecircumferential direction groove 20 is preferably from 4.0 mm to 9.2 mmin order to achieve a high degree of both water expelling performance,and braking performance and steering stability on dry road surfaces andicy/snowy road surfaces.

Note that in the pneumatic tire 10 of the present exemplary embodiment,the negative ratio of the tread face 12A of the tread 12 (the proportionof the groove area within the tread face 12A of the tread 12 withrespect to the area of the tread face 12A of the tread 12) is preferablyset from 33% to 40% in order to achieve a high degree of both waterexpelling performance, and braking performance and steering stability ondry road surfaces and icy/snowy road surfaces. In order for the luggrooves 16 to sufficiently function as main water flow paths, the groovearea of the lug grooves 16 is preferably greater than that of theshoulder-side circumferential direction grooves 20, and 50% or more ofthe total groove area is preferably the groove area of the lug grooves16.

Second Exemplary Embodiment

Next, explanation follows regarding a pneumatic tire 10 according to asecond exemplary embodiment of the present invention, with reference toFIG. 5. Note that configurations the same as those of the firstexemplary embodiment are appended with the same reference numerals, andexplanation thereof is omitted.

As illustrated in FIG. 5, in the lug grooves 16 of the pneumatic tire 10of the present exemplary embodiment, the groove side-wall 16F on thetread-in side and the groove side-wall 16K on the kick-off side areformed with plural straight line portions.

Similarly to in the first exemplary embodiment, A1 is set to be lessthan B1, and A2 is set to be less than B2 in the pneumatic tire 10 ofthe present exemplary embodiment too, thereby enabling the blockrigidity of each block to be increased while securing the groove volumenecessary for water expelling performance of the lug groove 16.

Third Exemplary Embodiment

Next, explanation follows regarding a pneumatic tire 10 according to athird exemplary embodiment of the present invention, with reference toFIG. 6. Note that configurations the same as those of the firstexemplary embodiment are appended with the same reference numerals, andexplanation thereof is omitted.

As illustrated in FIG. 6, in the lug grooves 16 of the pneumatic tire 10of the present exemplary embodiment, the radius of curvature Ra of thecircular arc shaped portion of the tread-in side second inclined portion16Fb and the radius of curvature Rb of the circular arc shaped portionof the kick-off side second inclined portion 16Kb are set larger than inthe first exemplary embodiment, and the circular arc shaped portion ofthe tread-in side second inclined portion 16Fb and the circular arcshaped portion of the kick-off side second inclined portion 16Kb areconnected smoothly to each other.

Similarly to in the first exemplary embodiment, A1 is set to be lessthan B1, and A2 is set to be less than B2 in the pneumatic tire 10 ofthe present exemplary embodiment too, thereby enabling the blockrigidity of each block to be increased while securing the groove volumenecessary for water expelling performance of the lug groove 16.

Further, the block rigidity in the present exemplary embodiment can beraised to a greater extent than in the first exemplary embodiment due tothe radius of curvature Ra and the radius of curvature Rb being setlarger than in the first exemplary embodiment.

Fourth Exemplary Embodiment

Next, explanation follows regarding a pneumatic tire 10 according to afourth exemplary embodiment of the present invention, with reference toFIG. 7 to FIG. 10. Note that configurations the same as those of thefirst exemplary embodiment are appended with the same referencenumerals, and explanation thereof is omitted.

As illustrated in FIG. 7, in the pneumatic tire 10 of the presentexemplary embodiment, the average of the groove depth D1 between theintersection point P1 and the intersection point P3 (directly under the⅓ point P2) of the groove bottom 16B of the lug groove 16 is set to beno less than 90% of the groove depth D0 of the end portion of the luggroove 16 on the tire equatorial plane CL side.

In cases in which in the groove depth of the lug groove 16 is set suchthat D1≤90% D0 in this manner, as illustrated in FIG. 7 and FIG. 8,raised-bottom portions 32 projecting from the groove bottom 16B to givea shallower groove depth are preferably provided in the sipes 28disposed at the tire width direction outer side of the ⅓ point P2,namely inside the sipes 28 of the shoulder-side block 26 in the presentexemplary embodiment, in order to increase the block rigidity of theshoulder-side blocks 26.

As illustrated in FIG. 7 and FIG. 8, a length L′ of the raised-bottomportions 32 provided at the sipes 28 is preferably set to no less than1.5 mm in order to increase block rigidity.

As illustrated in FIG. 7, a height dimension h of the raised-bottomportion 32 (measured from the groove bottom of the sipe 28) is smallerthan the groove depth dimension of the sipe 28, and the position of anapex of the raised-bottom portion 32 is lower than the tread face 12A ofthe tread 12 (namely, at the tire radial direction inside). In thepresent exemplary embodiment, two of the raised-bottom portions 32 areprovided in each sipe 28; however, it is sufficient if at least one isprovided, and three or more may be provided, and the raised-bottomportions 32 may be provided at locations where increasing block rigidityis desired.

As illustrated in FIG. 7 and FIG. 8, plural sipes 28 are formed in eachshoulder-side block 26 so as to extend from the tire width directioninner side end toward the tire width direction outer side and traversethe ground contact edge 12E. In cases in which the sipes 28 have agroove depth 60% or greater of the groove depth of the lug groove 16, itis preferable that at least half of the sipes 28 out of the plural sipes28 are provided with raised-bottom portions 32 (first raised-bottomportions of the present invention) having a height h of from 2 mm to 4mm within a range from the ground contact edge 12E to 20 mm toward thetire width direction inner side in order to increase the block rigidityon the ground contact edge 12E side of the shoulder-side block 26. Theadvantageous effect of increased block rigidity would be insufficientwere the height h of the raised-bottom portions 32 less than 2 mm, andblock rigidity would be too high locally were the height h of theraised-bottom portions 32 over 4 mm.

Moreover, it is preferable that the raised-bottom portions 32 (secondraised-bottom portions of the present invention) be provided within arange of 40% of a ground contact width (in the tire width direction) ofthe shoulder-side blocks 26 from the tire width direction inner side endtoward the ground contact edge 12E side of the shoulder-side blocks 26in order to increase the block rigidity of the shoulder-side blocks 26on the tire width direction inner side. Note that it is preferable thatthe height of the raised-bottom portions 32 provided within a range of40% of the ground contact width (in the tire width direction) of theshoulder-side blocks 26 from the tire width direction inner side endtoward the ground contact edge 12E side of the shoulder-side blocks 26be from 2 mm to 5 mm.

As illustrated in FIG. 8, in cases in which the raised-bottom portions32 are provided at each sipe 28 within a range of 40% of the groundcontact width BW (in the tire width direction) of the shoulder-sideblocks 26 from the tire width direction inner side end toward the groundcontact edge 12E side of the shoulder-side blocks 26, and theraised-bottom portions 32 form a row in a straight line shape along onedirection such that block rigidity might become too high locally,although omitted from illustration, it is preferable that sipes 28provided with raised-bottom portions 32 having high heights (forexample, raised-bottom portions 32 having a 5 mm height) and sipes 28provided with raised-bottom portions 32 having low heights relative tothe raised-bottom portions 32 having high heights (for example,raised-bottom portions 32 having a 2 mm height) are disposed alternatelyin the tire circumferential direction. This enables the block rigidityof the tire width direction inner side portions of the shoulder-sideblocks 26 to be raised appropriately, enabling anti-wear characteristicsof the shoulder-side blocks 26 to be improved.

Further, in cases in which plural sipes 28 provided with theraised-bottom portions 32 are formed on the shoulder-side blocks 26, andthe raised-bottom portions 32 form a row in a straight line shape alongone direction such that the block rigidity might become too highlocally, as illustrated in FIG. 9, local increases in block rigidity canbe suppressed and block rigidity can be increased appropriately bydisposing the sipes 28 provided with raised-bottom portions 32 and sipes28 that are not provided with raised-bottom portions 32 alternately inthe tire circumferential direction.

Moreover, in cases in which plural sipes 28 provided with theraised-bottom portions 32 are arrayed in the tire circumferentialdirection, as illustrated in FIG. 10, local increases in block rigiditycan be suppressed and block rigidity can be increased appropriately byarranging a raised-bottom portion 32 of one of the sipes 28 and araised-bottom portion 32 of another of the sipes 28 so as to be offsetfrom each other in the tire width direction such that the raised-bottomportions 32 of adjacent sipes 28 in the tire circumferential directionare not alongside each other in the tire circumferential direction.

Fifth Exemplary Embodiment

Next, explanation follows regarding a pneumatic tire 10 according to afifth exemplary embodiment of the present invention, with reference toFIG. 11. Note that configurations the same as those of the exemplaryembodiments described above are appended with the same referencenumerals, and explanation thereof is omitted.

As illustrated in FIG. 11, in the lug groove 16 of the pneumatic tire 10of the present exemplary embodiment, a parallel portion 16Bb having aconstant groove depth where the tread face 12A and the groove bottom 16Bare parallel to each other is provided from the ground contact edge 12Etoward the tire width direction inner side, and an inclined portion 16Bainclined in a direction of deepening groove depth is provided at a tirewidth direction inner side of the parallel portion 16Bb. Note that fromthe tire width direction inner side end of the inclined portion 16Batoward the tire equatorial plane CL side, the tread face 12A and thegroove bottom 16B are parallel to each other and set with a constantgroove depth. Note that in the present exemplary embodiment too, theaverage of the angle of inclination θ1 of the groove bottom 16B of thelug groove 16 from the intersection point P1 to the intersection pointP3 with respect to the tread face 12A contacting the road surface 31 isset to no more than 5°.

Between the intersection point P1 and the intersection point P3, thegroove bottom 16B of the lug groove 16 of the pneumatic tire 10 of thepresent exemplary embodiment is not inclined at a constant angle, andthe parallel portion 16Bb that runs parallel to the tread face 12A isprovided on the ground contact edge 12E side. However, the average angleof inclination of the groove bottom 16B of the lug groove 16 from theintersection point P1 to the intersection point P3 is set to be no morethan 5°, and in the vicinity of the ground contact edge 12E, the groovebottom 16B is parallel to the tread face 12A (road surface 31) and has aconstant groove depth. Thus, water taken into the lug groove 16 flowssmoothly in the vicinity of the ground contact edge 12E and turbulentflow does not occur, and is expelled from the ground contact edge 12Etoward the outside of the ground contact plane.

Other Exemplary Embodiments

Explanation has been given of some exemplary embodiments of the presentinvention; however, the present invention is not limited thereto.Obviously various other modifications may be implemented within a rangenot departing from the spirit of the present invention.

In the lug groove 16, as a minimum, is it sufficient to set at least oneout of A1<B1 or A2<B2. The cross-section profile of the lug groove 16,namely, the cross-section profiles of the groove side-wall 16F on thetread-in side, the groove side-wall 16K on the kick-off side, and thegroove bottom 16B are not limited to those illustrated in FIGS. 4, 5,and 6, and may be formed by curved lines other than circular arcs, orsubjected to various modifications. Further, in a comparison of theratio B1/A1 to the ratio B2/A2, the ratio B1/A1 may be set greater thanthe ratio B2/A2, or the ratio B1/A1 may be set equal to the ratio B2/A2.

Test Example 1

To verify the advantageous effects of the present invention, prototypesof a conventional example, a comparative example, and tires 1 to 5 ofExamples applied with the present invention were produced. Each of thetires had the tread pattern illustrated in FIG. 1, while the shapes ofthe groove bottoms of the lug grooves in the vicinity of the groundcontact edge differed from each other. Note that in Examples 1 to 4, thesipes did not include raised-bottom portions, and in Example 5, thesipes were provided with raised-bottom portions.

The following tests were performed on each tire to evaluate hydroplaningperformance (water expelling performance) on a wet road surface, brakingperformance on a dry road surface, and anti-wear characteristics.

Explanation follows regarding the test tires.

Conventional Example

the lug grooves were set to a constant groove depth of 9 mm from the endportion on the tire equatorial plane side to the ⅓ point, and the groovebottom was inclined at an angle of 6° from the ⅓ point toward the groundcontact edge.

Example 1

a constant groove depth of 9 mm was set from the end portion on the tireequatorial plane side to the ⅓ point, and the groove bottom was inclinedat an angle of 5° from the ⅓ point toward the ground contact edge.

Example 2

a constant groove depth of 9 mm was set from the end portion on the tireequatorial plane side to the ⅓ point, and the groove bottom was inclinedat an angle of 1° from the ⅓ point toward the ground contact edge.

Comparative Example 1

the lug grooves were set to a constant groove depth of 9 mm from the endportion on the tire equatorial plane side toward the ground contactedge.

Example 3

As illustrated in FIG. 11, the parallel portion 16Bb having a constantgroove depth in the vicinity of the ground contact edge 12E was providedat the groove bottom 16B of the lug grooves 16, and the inclined portion16Ba inclined in the direction of deepening groove depth was provided ata tire width direction inner side of the parallel portion 16Bb. Notethat the groove bottom 16B was inclined 3° (the average angle ofinclination θ1) from the ⅓ point toward the ground contact edge. InExample 3, the length of the parallel portion 16Bb as measured in thegroove length direction was 12 mm, the length of the inclined portion16Ba as measured in the groove length direction was 12 mm, and an angleof inclination θa of the inclined portion 16Ba was 5° (the measurementreference was the same as that of the angle of inclination θ1).

Example 4

Similarly to in Example 3, the parallel portion 16Bb and the inclinedportion 16Ba were provided at the groove bottom 16B of the lug groove16. Note that the groove bottom 16B was inclined 3° (the average angleof inclination θ1) from the ⅓ point toward the ground contact edge. InExample 4, the length of the parallel portion 16Bb as measured in thegroove length direction was 18 mm, the length of the inclined portion16Ba as measured in the groove length direction was 6 mm, and the angleof inclination θa of the inclined portion 16Ba was 3° (the measurementreference was the same as that of the angle of inclination θ1).

Example 5

The tire of Example 3 where raised-bottom portions were provided at thesipes.

Hydroplaning Performance (Straight Line)

Test tires with a tire size of 195/65R15 were each assembled onto anapplicable rim, inflated to an internal pressure of 200 kPa, and mountedto a right front wheel of a passenger vehicle. The right side of thevehicle was set on a road surface covered with depth of 10 mm of water.The vehicle was accelerated, and the speed at which the tires skiddedwas taken as the speed at which hydroplaning occurred.

The evaluation is expressed using relative values in an index where thespeed at which hydroplaning occurs in the tire according to theconventional example was set to 100. The larger the numerical value, thehigher the speed at which hydroplaning occurred and the better thehydroplaning performance.

Dry Road Surface Braking Performance

The tires with a tire size of 195/65R15 were each assembled onto anapplicable rim, and braking distance was calculated using deceleration(G) until coming to a stop after applying the brakes at 100 km/h.

The evaluation is expressed using an inverse index, with the brakingdistance of the conventional example set to 100. The larger thenumerical value, the shorter the braking distance and the better thebraking performance.

Anti-Wear Characteristics

The tires with a tire size of 195/65R15 were each assembled onto anapplicable rim, inflated to the specified internal pressure for thevehicle to which they were mounted (200 kPa), and loaded to thespecified standard load (4.3 kN). The wear life of each tire wasestimated from the wear amount after running for 5000 km on a drumtesting machine. Note that the wear life is considered to be the timewhen any of the main grooves on the tire is completely worn away.

The evaluation is expressed using an index, with the wear life of thetire of the conventional example set to 100. The larger the numericalvalue, the better the anti-wear characteristics.

TABLE 1 Conventional Comparative Example Example 1 Example 2 ExampleExample 3 Example 4 Example 5 Hydroplaning Performance 100 103 104 103104 102 104 (Straight Line) Braking Performance (Dry 100 107 103 98 109104 113 Road Surface) Anti-Wear Characteristics 100 113 105 96 116 107123

As illustrated in Table 1, the tires of Examples 1 to 5 applied with thepresent invention exhibited excellent hydroplaning performance, brakingperformance, and anti-wear characteristics.

The disclosure of Japanese Patent Application No. 2015-120368, filed onJun. 15, 2015 is incorporated in its entirety by reference herein.

All cited documents, patent applications, and technical standardsmentioned in the present specification are incorporated by reference inthe present specification to the same extent as if the individual citeddocument, patent application, or technical standard was specifically andindividually indicated to be incorporated by reference.

The invention claimed is:
 1. A pneumatic tire, comprising: a tread thatcontacts a road surface; a plurality of lug grooves that are provided atthe tread, that extend from a tire width direction center side of thetread toward a ground contact edge of the tread, and that partition aland portion; and a plurality of shoulder-side circumferential directiongrooves, each of which couples together one of the plurality of luggrooves and another of the plurality of lug grooves, which are adjacentto each other in a tire circumferential direction, wherein, when viewinga cross-section of each of the lug grooves along a groove lengthdirection, in a state in which the tire is mounted to an applicable rimand inflated to a maximum air pressure corresponding to a tire standardmaximum load capacity, while applied with a load of 100% of the maximumload capacity in a state in which a tire rotation axis is, with respectto a horizontal and flat road surface, parallel to the road surface:each of the lug grooves includes a groove bottom formed at an inclinewith respect to a tread face of the tread contacting the road surface,such that a groove depth at a ground contact edge side of the luggrooves becomes shallower in depth on progression from a tire equatorialplane side toward the ground contact edge; and an average angle ofinclination θ1 formed between the tread face and the groove bottom ofthe lug grooves from an intersection point P1 to an intersection pointP3 is set to be no more than 5°, P1 being an intersection point betweenthe groove bottom of the lug grooves and an imaginary line passingthrough the ground contact edge and extending in a direction at a rightangle to the tread face, P3 being an intersection point between thegroove bottom of the lug grooves and an imaginary line passing through a⅓ point P2 on the tread face and extending in a direction at a rightangle to the tread face, and P2 being ⅓ of the distance of a treadhalf-width from the ground contact edge toward the tire equatorial planeside, wherein a ratio b/c is 0.07 or more and 0.60 or less, wherein b isa cross-sectional area of a connecting portion between one tirecircumferential direction side end portion of one of the plurality ofshoulder-side circumferential direction grooves and one of the pluralityof lug grooves, and c is a cross-sectional area of the one of theplurality of lug grooves at the ground contact edge, and wherein thetread is formed with different kinds of shoulder-side blocks in acircumferential direction dimension, and a radius of curvature Ra on atread-in side and a radius of curvature Rb on a kick-off side of the luggrooves partitioning the shoulder-side blocks having a shortcircumferential direction dimension are larger than a radius ofcurvature Ra on the tread-in side and a radius of curvature Rb on thekick-off side of the lug grooves partitioning the shoulder-side blockshaving a long circumferential direction dimension.
 2. The pneumatic tireof claim 1, wherein: the land portion partitioned by the plurality oflug grooves is further partitioned into a plurality of blocks in a tirewidth direction by a plurality of circumferential direction groovesextending in a direction intersecting the lug grooves; a plurality ofsipes are formed at blocks among the plurality of blocks that includethe ground contact edge; and at least half of the plurality of sipes areprovided with a second raised-bottom portion having a height of from 2mm to 5 mm within a range spanning from a tire width direction innerside end of the blocks to a position 40% of the distance from the tirewidth direction inner side end toward the ground contact edge of theblock.
 3. The pneumatic tire of claim 1, wherein: a flat portion, havinga constant groove depth from the ground contact edge toward a tire widthdirection inner side, is provided at the groove bottoms, a plurality ofsipes are formed in the land portion including the ground contact edge,the plurality of sipes being formed so as to extend from a tire widthdirection inner side end of the land portion toward a tire widthdirection outer side and to traverse the ground contact edge, and atleast half of the plurality of sipes are provided with a firstraised-bottom portion having a height of from 2 mm to 4 mm within arange from the ground contact edge to 20 mm toward the tire widthdirection inner side.
 4. The pneumatic tire of claim 1, wherein: a flatportion, having a constant groove depth from the ground contact edgetoward a tire width direction inner side, is provided at the groovebottoms, the land portion partitioned by the plurality of lug grooves isfurther partitioned into a plurality of blocks in a tire width directionby a plurality of circumferential direction grooves extending in adirection intersecting the lug grooves, a plurality of sipes are formedat blocks among the plurality of blocks that include the ground contactedge, and at least half of the plurality of sipes are provided with asecond raised-bottom portion having a height of from 2 mm to 5 mm withina range spanning from a tire width direction inner side end of theblocks to a position 40% of the distance from the tire width directioninner side end toward the ground contact edge of the block.
 5. Thepneumatic tire of claim 1, wherein: a plurality of sipes are formed inthe land portion including the ground contact edge, the plurality ofsipes being formed so as to extend from a tire width direction innerside end of the land portion toward a tire width direction outer sideand to traverse the ground contact edge, at least half of the pluralityof sipes are provided with a first raised-bottom portion having a heightof from 2 mm to 4 mm within a range from the ground contact edge to 20mm toward the tire width direction inner side, the land portionpartitioned by the plurality of lug grooves is further partitioned intoa plurality of blocks in a tire width direction by a plurality ofcircumferential direction grooves extending in a direction intersectingthe lug grooves, a plurality of sipes are formed at blocks among theplurality of blocks that include the ground contact edge, and at leasthalf of the plurality of sipes are provided with a second raised-bottomportion having a height of from 2 mm to 5 mm within a range spanningfrom a tire width direction inner side end of the blocks to a position40% of the distance from the tire width direction inner side end towardthe ground contact edge of the block.
 6. The pneumatic tire of claim 1,wherein: a flat portion, having a constant groove depth from the groundcontact edge toward a tire width direction inner side, is provided atthe groove bottoms, a plurality of sipes are formed in the land portionincluding the ground contact edge, the plurality of sipes being formedso as to extend from a tire width direction inner side end of the landportion toward a tire width direction outer side and to traverse theground contact edge, at least half of the plurality of sipes areprovided with a first raised-bottom portion having a height of from 2 mmto 4 mm within a range from the ground contact edge to 20 mm toward thetire width direction inner side, the land portion partitioned by theplurality of lug grooves is further partitioned into a plurality ofblocks in a tire width direction by a plurality of circumferentialdirection grooves extending in a direction intersecting the lug grooves,a plurality of sipes are formed at blocks among the plurality of blocksthat include the ground contact edge, and at least half of the pluralityof sipes are provided with a second raised-bottom portion having aheight of from 2 mm to 5 mm within a range spanning from a tire widthdirection inner side end of the blocks to a position 40% of the distancefrom the tire width direction inner side end toward the ground contactedge of the block.
 7. The pneumatic tire of claim 1, wherein across-sectional area a is from 0 mm² to 18 mm², the cross-sectional areab is from 8 mm² to 46 mm², and the cross-sectional area c is from 77 mm²to 110 mm², wherein a is a cross-sectional area at a connection portionof the lug groove to a center circumferential direction groove.
 8. Thepneumatic tire of claim 1, wherein an average of the groove depthbetween the intersection point P1 and the intersection point P3 of thegroove bottom of the lug groove is no less than 90% of a groove depth D0of an end portion of the lug groove on the tire equatorial plane side.9. The pneumatic tire of claim 1, wherein a groove area of the luggrooves is greater than that of the shoulder-side circumferentialdirection grooves.
 10. A pneumatic tire, comprising: a tread thatcontacts a road surface; a plurality of lug grooves that are provided atthe tread, that extend from a tire width direction center side of thetread toward a ground contact edge of the tread, and that partition aland portion; and a plurality of shoulder-side circumferential directiongrooves, each of which couples together one of the plurality of luggrooves and another of the plurality of lug grooves, which are adjacentto each other in a tire circumferential direction, wherein, when viewinga cross-section of each of the lug grooves along a groove lengthdirection, in a state in which the tire is mounted to an applicable rimand inflated to a maximum air pressure corresponding to a tire standardmaximum load capacity while in a non-loaded state: each of the luggrooves has a groove bottom formed at an incline with respect to a treadface of the tread, such that a groove depth at a ground contact edgeside of the lug grooves becomes shallower in depth on progression from atire equatorial plane side toward the ground contact edge; and anaverage angle of inclination θ2 formed between the tread face betweenthe ground contact edge and a ⅓ point P2, and the groove bottom betweenan intersection point P1 and an intersection point P3, is set to be nomore than 5°, P1 being an intersection point between the groove bottomof the lug grooves and an imaginary line passing through the groundcontact edge and extending in a direction at a right angle to the treadface, P3 being an intersection point between the groove bottom of thelug grooves and an imaginary line passing through the ⅓ point P2 on thetread face and extending in a direction at a right angle to the treadface, and P2 being ⅓ of the distance of a tread half-width from theground contact edge toward a tire equatorial plane side, wherein a ratiob/c is 0.07 or more and 0.60 or less, wherein b is a cross-sectionalarea of a connecting portion between one tire circumferential directionside end portion of one of the plurality of shoulder-sidecircumferential direction grooves and one of the plurality of luggrooves, and c is a cross-sectional area of the one of the plurality oflug grooves at the ground contact edge, and wherein the tread is formedwith different kinds of shoulder-side blocks in a circumferentialdirection dimension, and a radius of curvature Ra on a tread-in side anda radius of curvature Rb on a kick-off side of the lug groovespartitioning the shoulder-side blocks having a short circumferentialdirection dimension are larger than a radius of curvature Ra on thetread-in side and a radius of curvature Rb on the kick-off side of thelug grooves partitioning the shoulder-side blocks having a longcircumferential direction dimension.
 11. The pneumatic tire of claim 10,wherein: the land portion partitioned by the plurality of lug grooves isfurther partitioned into a plurality of blocks in a tire width directionby a plurality of circumferential direction grooves extending in adirection intersecting the lug grooves, a plurality of sipes are formedat blocks among the plurality of blocks that include the ground contactedge, and at least half of the plurality of sipes are provided with asecond raised-bottom portion having a height of from 2 mm to 5 mm withina range spanning from a tire width direction inner side end of theblocks to a position 40% of the distance from the tire width directioninner side end toward the ground contact edge of the block.
 12. Thepneumatic tire of claim 10, wherein: a flat portion, having a constantgroove depth from the ground contact edge toward a tire width directioninner side, is provided at the groove bottoms, a plurality of sipes areformed in the land portion including the ground contact edge, theplurality of sipes being formed so as to extend from a tire widthdirection inner side end of the land portion toward a tire widthdirection outer side and to traverse the ground contact edge, and atleast half of the plurality of sipes are provided with a firstraised-bottom portion having a height of from 2 mm to 4 mm within arange from the ground contact edge to 20 mm toward the tire widthdirection inner side.
 13. The pneumatic tire of claim 10, wherein: aflat portion, having a constant groove depth from the ground contactedge toward a tire width direction inner side, is provided at the groovebottoms, the land portion partitioned by the plurality of lug grooves isfurther partitioned into a plurality of blocks in a tire width directionby a plurality of circumferential direction grooves extending in adirection intersecting the lug grooves, a plurality of sipes are formedat blocks among the plurality of blocks that include the ground contactedge, and at least half of the plurality of sipes are provided with asecond raised-bottom portion having a height of from 2 mm to 5 mm withina range spanning from a tire width direction inner side end of theblocks to a position 40% of the distance from the tire width directioninner side end toward the ground contact edge of the block.
 14. Thepneumatic tire of claim 10, wherein: a plurality of sipes are formed inthe land portion including the ground contact edge, the plurality ofsipes being formed so as to extend from a tire width direction innerside end of the land portion toward a tire width direction outer sideand to traverse the ground contact edge, at least half of the pluralityof sipes are provided with a first raised-bottom portion having a heightof from 2 mm to 4 mm within a range from the ground contact edge to 20mm toward the tire width direction inner side, the land portionpartitioned by the plurality of lug grooves is further partitioned intoa plurality of blocks in a tire width direction by a plurality ofcircumferential direction grooves extending in a direction intersectingthe lug grooves, a plurality of sipes are formed at blocks among theplurality of blocks that include the ground contact edge, and at leasthalf of the plurality of sipes are provided with a second raised-bottomportion having a height of from 2 mm to 5 mm within a range spanningfrom a tire width direction inner side end of the blocks to a position40% of the distance from the tire width direction inner side end towardthe ground contact edge of the block.
 15. The pneumatic tire of claim10, wherein: a flat portion, having a constant groove depth from theground contact edge toward a tire width direction inner side, isprovided at the groove bottoms, a plurality of sipes are formed in theland portion including the ground contact edge, the plurality of sipesbeing formed so as to extend from a tire width direction inner side endof the land portion toward a tire width direction outer side and totraverse the ground contact edge, at least half of the plurality ofsipes are provided with a first raised-bottom portion having a height offrom 2 mm to 4 mm within a range from the ground contact edge to 20 mmtoward the tire width direction inner side, the land portion partitionedby the plurality of lug grooves is further partitioned into a pluralityof blocks in a tire width direction by a plurality of circumferentialdirection grooves extending in a direction intersecting the lug grooves,a plurality of sipes are formed at blocks among the plurality of blocksthat include the ground contact edge, and at least half of the pluralityof sipes are provided with a second raised-bottom portion having aheight of from 2 mm to 5 mm within a range spanning from a tire widthdirection inner side end of the blocks to a position 40% of the distancefrom the tire width direction inner side end toward the ground contactedge of the block.
 16. The pneumatic tire of claim 10, wherein across-sectional area a is from 0 mm² to 18 mm², the cross-sectional areab is from 8 mm² to 46 mm², and the cross-sectional area c is from 77 mm²to 110 mm², wherein a is a cross-sectional area at a connection portionof the lug groove to a center circumferential direction groove.
 17. Thepneumatic tire of claim 10, wherein an average of the groove depthbetween the intersection point P1 and the intersection point P3 of thegroove bottom of the lug groove is no less than 90% of a groove depth D0of an end portion of the lug groove on the tire equatorial plane side.18. The pneumatic tire of claim 10, wherein a groove area of the luggrooves is greater than that of the shoulder-side circumferentialdirection grooves.